[sdiy] Mysterious Transformer Wire

[Glen]

Are power transformers ever made with a wire that doesn't connect to any of
the windings, neither primary nor secondary?

I am looking at an old transformer that I salvaged from an old Kimball
organ, and there is a fairly small gauge blue wire that was originally
connected to ground, before I removed the transformer from its chassis. I
first thought that this wire might be a center tap for one of the
secondaries, but it's much smaller in gauge than any of the secondaries. It
also has no DC electrical connection to any of the secondaries.

The primary has a tap to allow for operation from different mains voltages.
The "220 VAC" connection was not connected to anything. (This was a 117 VAC
organ.)

Judging from some old service manuals, I feel confident that I've correctly
identified the 3 different primary wires. I have identified one secondary
winding that was used to power a string of 6V lamps. I have also identified
another secondary that has 7 connections, including a center tap.

The only thing remaining is this small-gauge blue wire, which was
originally grounded. I can't measure any DC continuity between it and any
of the other transformer wires. I also can't measure any DC continuity
between it and the housing of the transformer. I also can't find any
mention of it in the service manuals.

Any suggestions?

The transformer did pass the smoke test, at least it did when I hooked it
up without a load. All the identified secondaries had appropriate AC
voltages present. The odd thing, is that, with my DMM, I could measure AC
voltage between the blue wire and the two secondaries, even though there is
no measurable DC connection between the blue wire and anything else on this
crazy transformer. If the blue wire is for a shield of some sort, should it
do that? Oh yeah, this transformer does have an outer metal cover
(shielding), in case you were wondering, but it doesn't seem to be
connected to the mysterious blue wire.  


thanks,
Glen